The present invention relates to flexible circuits and more particularly to flexible circuits utilized in the automotive industry which can additionally incorporate relays for circuits.
In the most recent quarter century the utilization of electronics in automotive vehicles has increased significantly. For example virtually all automotive vehicles have an engine control module to optimize the performance of the engine with regard to fuel efficiency and environmental emissions. Inflatable restraints have been added to enhance occupant safety in a crash situation. Advanced braking systems, such as anti-skid braking and traction control further enhance safe operation of the vehicle. Other electrical systems have been added or enhanced to increase the comfort of the vehicle. The above mentioned additions and enhancements have resulted in a more complex wiring system which supplies power and signal transfer to and from various electrical components and controllers. Currently, much of the power and signaling requirements of a vehicle are supplied by hard conductive wiring, which is housed in a wiring harness. Fabrication of a wiring harness is a very labor intensive operation. Installation and/or repair of a wiring harness can also be very time consuming and expensive. Another disadvantage associated with the hard copper conductive wiring is the cost associated with the copper. For certain applications the copper wire needed to provide for signal transfer at a low electrical load can be provided by a copper wire of a very small cross-sectional area. However, a minimum diameter of copper wiring is not determined by its electrical requirements. The minimum diameter of the wiring is determined by its frailty during the assembly process of the wiring harness and of the wiring of the vehicle.
To reduce the cost of automotive wiring harnesses a new type of electrical conduit has been provided. This new conduit is typically referred to as a flexible circuit. In a flexible circuit, a polymeric (or insulated metallic ribbon) substrate which is flexible, provides support for the various electrical conductor lines. The electrical conductors are then supplied by a foil that is affixed to the flexible substrate. Another flexible layer of polymeric material can cover the conductors on the flexible substrate.
The utilization of flexible circuits as a replacement for the prior wiring harnesses has been limited due to the particular problems faced by flexible circuits at the various component interfaces. For instance, the interface of the flexible circuit with a fuse box has been a particular limiting factor. To overcome those limitations, an inventive contact method has been provided in U.S. Pat. No. 6,302,704 filed Apr. 22, 1999. Other examples of connector interfaces for flexible circuits can be found in a review of U.S. Pat. Nos. 5,885,091 and 5,969,418.
Another problem with the utilization of flexible circuits is in the use of relays. Relays are typically switches that have two contacts which are spring biased toward or away from each other, and are activated (closed or opened) by an electromagnetic force by a selectively excitable electromagnetic coil. Relays are typically provided for high current applications that require momentary application. Relays are commonly self-contained entities that contain a coil and contacts. Relays are typically prepackaged to a predetermined physical footprint. The design of relays is mostly controlled by their manufacturers and users of such relays adapt their circuits to predesigned physical specifications. Two major elements in the design of relays are the generation of high current contact heat between the contacts, and the amount of current which is allowed in the exciting coil which is typically of a much lower current. Because of the current capabilities of the contacts of the relay, most relays have a solid post with a relatively high mass. The relay coil is typically specified to be excited by a low current and therefore has very low mass copper wires. When connecting the relay to a conventional circuit board the high relative mass of the relay terminals provides a relatively large heat sink so that lots of heat is required to assemble the relay to the remainder of the circuit. This heat required for assembly is typically within the limits of a rigid circuit board. However, with a flexible circuit no such rigid circuit board is provided and items such as relays which require a high heat input are difficult to assemble to the flexible circuit. Providing the heat required for many relays causes the flexible circuit to become warped and deformed.
Prior to the present invention, to accommodate the heat of assembly the flexible circuit often has to be redesigned to be a non-planar structure with a much larger mass than desirable. Such a modification of the flexible circuit diminishes its many advantages. Flexibility of the flexible circuit is especially important in applications of engine control modules which often have physically large circuits which are folded over for placement within a mounting box to conserve space within the engine compartment of the vehicle.
It is desirable to provide a flexible circuit which allows for the relatively higher current contacts in connecting one circuit to another that is typically required in the utilization of a relay without having a flexible circuit with an increased mass which will diminish its characteristics of flexibility. It is furthermore even more desirable to have an arrangement of a flex circuit relay which can eliminate the requirements of a coil member.
In a preferred embodiment an arrangement of a flex circuit relay is provided. A first substrate is provided which may be a flex circuit or a conventional rigid circuit board. A pair of gapped conductive members which may be tracings or surface mounted devices are also provided connected on the first substrate. A second flexible substrate is provided. The second flexible substrate is supported away from the first substrate. The second substrate has a contact portion. Connected to the contact portion is a conductive member which may be a connective member provided by an etched conductor or by a surface mounted device.
In a first position with respect to the first substrate, the contact portion of the second substrate is spaced away from the first substrate. In a second position with respect to the first substrate, the contact portion of the second substrate is spaced adjacent to the first substrate. A piezoelectric actuator is connected to the second substrate which enables the second substrate contact portion to move between the first and second positions with respect to the first substrate. When moved to the second position adjacent to the first substrate, the second conductive member bridges the gap between the pair of conductive members of the first substrate to complete the circuit. The flex circuit relay of the present invention can be configured to be normally on or normally off.
An advantage of the present invention is that the piezoelectric actuator eliminates the use for a coil and provides a relay typically having a much thinner profile than a relay device which utilizes a coil.
Other features and advantages of various embodiments of the present invention will become more apparent to those skilled in the art from the reading of the following detailed description and upon reference to the drawings.